A light emitting device using a light emitting diode chip has been conventionally proposed that is shown in FIGS. 18A and 18B. In the conventional device, the light emitting diode chip (hereinafter, referred to as LED chip) 1 is mounted on a metal mounting board 20 that includes a metal plate 21 made of a metal with a high thermal conductivity, e.g. aluminum, an insulating layer 22 made of an insulating resin material, e.g. glass epoxy and provided on a surface of the metal plate, and a wiring portion (wiring pattern) 23 that is a copper foil provided on the insulating layer 22.
The LED chip 1 is electrically connected with the wiring portion 23 through a bonding wire W. The LED chip 1 includes, for example, a sappshire substrate and a gallium nitride light emitting portion provided on the sapphire substrate.
The conventional light emitting device includes a frame member 30 that has a round hole around the LED chip 1. The frame member 30 is adhered to the metal mounting board 20 via an adhesive layer 40 (shown in FIG. 18B). The hole in the frame member 30 is filled with a transparent sealing resin such as epoxy resin, silicone resin, or the like, in which the LED chip 1 is encapsulated. Light emitted from the LED chip 1 is extracted forward (upward in FIG. 18A) through a resin seal portion 50 of the sealing resin filled in the hole in the frame member 30. The inside diameter of the round hole in the frame member 30 mainly decreases with distance from the top of the hole so that the hole has inverted trapezoidal cross section, but in the vicinity of the metal mounting board 20, the inside diameter increases toward the metal mounting board 20 as shown in FIG. 18B.
In the light emitting device, the LED chip 1 is mounted on the metal mounting board 20 with a high thermal conductivity that includes the metal plate 21 and the insulating layer 22 of about 100 μm thickness. Therefore, the light emitting device allows heat generated at the LED chip 1 to be easily radiated to the outside, as compared to a device where a surface mount LED having an LED chip therein is mounted on a circuit board. Thus, the light emitting device can advantageously protect the LED chip 1 from temperature rise that may cause decrease of the luminous efficiency, decrease of the operating life, and deterioration of the resin seal portion 50.
The frame member 30 is made of a white resin so that its inside wall 31 functions as a reflector. Light from the LED chip 1 can be reflected on the inside wall 31 of the frame member 30 to be directed forward, thus efficiently extracted from the light emitting device to the outside.
However, in the conventional light emitting device, the LED chip 1 is not mounted directly on the metal plate 21, but it is mounted over the metal plate with the insulating layer 22, which is lower in thermal conductivity than the metal plate 21 and has about 100 μm thickness, provided between them. Therefore, heat radiation of the light emitting device decreases, as compared to the case where the LED chip is mounted directly on the metal plate 21.
Additionally, the conventional light emitting device has the following disadvantage in the efficiency of light extraction from the LED chip 1. If the LED chip 1 is positioned deeper than the region of the round hole in the frame member 30 where the radius is the smallest, light from the LED chip 1 is partially blocked, thus failing to be extracted efficiently. With reference to the surface of the insulating layer 22, the surface of the LED chip 1 is at a height of about 80 μm, the thickness of the chip. The height H from the reference plane to the region of the frame member 30 where the radius of the hole is the smallest is about 300 μm that is the sum of the thickness of the adhesive layer 40, the thickness of the wiring portion 23 (the thickness of the copper foil), and the thickness of the portion of the frame member 30 where the inside diameter of the hole increases toward the metal mounting board. In other words, the inside wall 31 of the frame member 30 that functions as a reflector is located away as compared to the surface of the LED chip
1. Thus, efficient reflection of light cannot be provided.
In the case where the LED chip 1 has a transparent substrate such as sapphire substrate or the like, light emitted from the light emitting portion of the LED chip 1 is partially directed sideward. Therefore, the conventional light emitting device is disadvantageous in that light emitted sideward from the LED chip 1 fails to be efficiently extracted to the outside.
There may be a case where part of the insulating layer 22 is removed so that the LED chip 1 can be mounted on the metal plate 21 in order to improve heat radiation. In such a case, the thickness of portions that fail to function as a reflector (ineffective portions) increases by the thickness of the insulating layer 22 (about 100 μm), in addition to the height H. This further decreases the efficiency of extraction of light emitted sideward from the LED chip 1.
In the conventional light emitting device, the frame member 30 is made of a white resin for enhancing the light extraction efficiency. However, when heated in mounting process of the LED chip 1, the white resin may be oxidized to be colored, thus decreased in the reflecting ability. Further, in the case where an LED chip emitting blue light is employed as the LED chip 1, blue light emitted from the LED chip 1 may cause the frame member 30 of resin to deteriorate to be colored and thus decreased in the reflecting ability.
The present invention has been developed in view of the above mentioned problems, and it is an object of the present invention to provide a light emitting device that can enhance heat radiation while allowing light from a light emitting diode chip to be efficiently extracted to the outside, as compared to conventional devices.